1. Field of the Invention:
The invention relates to an offshore system, comprising a drilling vessel, e.g. a semi-submersible drilling vessel comprising a deck on which a drilling tower for performing drilling operations is mounted.
2. Background of the Invention:
Such an offshore system is well known and commonly used to perform drilling operations. The main disadvantage of such a system is that such a drilling vessel that can only perform drilling operations is inefficient when performing other operations and therefore has a high total running cost.
It is known to overcome this drawback by replacing the drilling tower by a multipurpose tower, as described in U.S. Pat. No. 6,871,609. Such a multipurpose tower can be used to perform maintenance operations, as well as drilling operations. This increases the efficiency of an offshore system.
In WO 2005/059297, WO 2004/020275, U.S. Pat. Nos. 6,932,553, 6,868,902, 6,763,898, 6,926,259 (in particular FIG. 13) by the present applicant specific designs of multipurpose towers and the use thereof is disclosed. The information and contents of these documents is herein incorporated by reference. Common prior art vessels are only suitable for drilling. US 2004/089215 by the present applicant discloses a vessel suitable for both drilling and well maintenance. The content of this application is also herein incorporated by reference.